A light-emitting diode (referred to hereinafter as LED) represents one of the most popular light-emitting devices today. In recent years, the luminous efficacy of LEDs, defined in lumens per Watt, has increased significantly from 20 lumens per Watt (approximately the luminous efficacy of an incandescent light bulb) to over 400 lumens per Watt, which greatly exceeds the luminous efficacy of a fluorescent light at 60 lumens per Watt. In other words, for a fixed amount of light output, LEDs consume approximately one sixth of the power compared to fluorescent lights, and almost negligibly small compared to incandescent light bulbs. Accordingly, it is not surprising today that lighting fixtures with LEDs have been replacing incandescent light bulbs and fluorescent light tubes. A new term “Solid-State Lighting” has been created. The term “Solid-State Lighting” refers to the type of lighting that uses semiconductor light-emitting diodes, such as an LED rather than traditional light sources.
Generally, LEDs are more expensive than conventional light sources. However, high reliability and low power consumption may be the main reasons for LEDs adoption in lighting. For example, LEDs are popular as light sources in warehouses, gasoline stations, and streetlights where replacement of the light sources would incur maintenance cost compared to the traditional light sources. In addition, savings from the low power consumption of the LEDs may justify the cost of the LEDs. For example, the power consumption of the LEDs may be less than 50% compared to conventional light sources and accordingly, the cost savings from long period of use may be more than the cost for the LEDs. Therefore, the reliability requirement for LEDs is generally high. Most LEDs are expected to be operable for more than 60,000 hours compared to less than 20,000 hours for conventional light sources such as fluorescent light tubes.
Like any other light sources, LEDs may produce heat and over long period of time, thermal expansion from the heat generated by the LEDs may stress the LEDs. In order to prolong the reliability of such LED lighting device, heat dissipating fins may be required. Installation of heat dissipating fins may increase the cost of the lighting devices. In addition, the requirement of heat dissipating fins may add weight to the lighting devices.